mebis Tafel:

<button id="btn" type="button" class="btn btn-success" data-toggle="modal" data-target=".bd-example-modal-lg" onclick="reloadFrame()">📝 Tafel</button><div class="modal fade bd-example-modal-lg" tabindex="-1" role="dialog" aria-labelledby="mebisTafel" aria-hidden="true">
<div class="modal-dialog modal-lg">
<div class="modal-content">
<div class="modal-header">  
<h4 class="modal-title" id="mebisTafel">mebis Tafel</h4>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div>
<iframe id="tafel" src="<https://tafel.mebis.bayern.de/frames>" style="width:100%;height:500px"></iframe>
</div></div>
</div>
</div>
<script>function reloadFrame(){
  document.getElementById('tafel').src = document.getElementById('tafel').src;
}
</script>

GeoGebra Notizen:

<button id="btn" type="button" class="btn btn-success" data-toggle="modal" data-target=".bd-example-modal-lg" onclick="reloadFrame()">📝 Tafel</button><div class="modal fade bd-example-modal-lg" tabindex="-1" role="dialog" aria-labelledby="mebisTafel" aria-hidden="true">
<div class="modal-dialog modal-lg">
<div class="modal-content">
<div class="modal-header">  
<h4 class="modal-title" id="mebisTafel">mebis Tafel</h4>
<button type="button" class="close" data-dismiss="modal" aria-label="Close">
<span aria-hidden="true">×</span>
</button>
</div>
<div>
<iframe id="tafel" src="<https://www.geogebra.org/notes?lang=de>" style="width:100%;height:500px"></iframe>
</div></div>
</div>
</div>
<script>function reloadFrame(){
  document.getElementById('tafel').src = document.getElementById('tafel').src;
}
</script>